There is increasing evidence that avian vocal learning exhibits many parallels with human vocal learning, both ethological and physiological. A broad comparative program of research is proposed in a search for innate constraints on vocal learning. Selective responsiveness will be analyzed comparatively using computer-synthesized stimuli. Avian perception of vocal stimuli will be studied by conditioning techniques for parallels with the categorical perception of speech sounds by human infants. Early stages of avian vocal development, which resemble the babbling stage of infant speech, will be analyzed comparatively for evidence of auditory template matching. The hypothesis of innate but modifiable sensory templates as a basis for vocal development, providing the logical framework for all phases of this research plan, is believed to be generalizable from avian vocal learning to speech development in infants.